Radio frequency (RF) front-end circuits like low noise amplifiers (LNAs) need to detect low-power signals and are therefore extremely sensitive by nature. A large noise spike, either in or close to the operating frequency band of the device, can de-sensitize the circuit and destroy its functionality. To prevent this problem, all radio architectures include filters and other narrow band circuits, which prevent the noise in the incoming spectrum from reaching the LNA. However, there are no systematic ways to filter noise from other sources, such as noise coupling through the power supply and appearing at the output of the LNA, where it can degrade the performance of the downstream circuits.
The sensitivity of RF circuits to power supply noise has resulted in difficulties for integration of digital and RF/analog sub-systems on packaging structures. One typical approach to isolate the sensitive RF/analog circuits from the noisy digital circuits is to split the power plane or both power and ground planes. The gap in power plane or ground plane can partially block the propagation of electromagnetic waves. For this reason, split planes are usually used to isolate sensitive RF/analog circuits from noisy digital circuits. Although split planes can block the propagation of electromagnetic waves, part of the electromagnetic energy can still couple through the gap. Due to the electromagnetic coupling, this method only provides a marginal isolation (i.e., −20 dB to −60 dB) at high frequencies (i.e., above ˜1 GHz) and becomes ineffective as the sensitivity of RF circuits increases and operating frequency of the system increases. At low frequencies (i.e., below ˜1 GHz), split planes provide an isolation of −70 dB to −80 dB.
In addition, split planes sometimes require separate power supplies to maintain the same DC level, which is not cost-effective. Therefore, the development of a better noise isolation method is needed for good performance of a system having a RF/analog circuit and a digital circuit.
Furthermore, as systems become more compact, multiple power supplies become a luxury that the designer cannot afford. The use of ferrite beads have been suggested as a solution to these problems, enabling increased isolation as well as the use of a single power supply. However, due to the high sensitivity of RF circuitry, the amount of isolation provided by ferrite beads again tends to be insufficient at high frequencies.
Electromagnetic bandgap (EBG) structures have become very popular due to their enormous applications for suppression of unwanted electromagnetic mode transmission and radiation in the area of microwave and millimeter waves. EBG structures are periodic structures in which propagation of electromagnetic waves is not allowed in a specified frequency band. In recent years, EBG structures have been proposed to suppress simultaneous switching noise (SSN) in a power distribution network (PDN) in high-speed digital systems for antenna applications. These EBG structures have a thick dielectric layer (60 mils to 180 mils) that exists between the power plane and the ground plane. In addition, these EBG structures require an additional metal layer with via connections. Thus, these EBG structures are expensive solutions for printed circuit board (PCB) applications.
Accordingly, there is a need in the industry to address the aforementioned deficiencies and/or inadequacies.